Preparing the DCPIP solutionWeigh out accurately approximately 0.24 g DCPIP (Mr = 268.1g/mol) and make up to 1 L with distilled water. This is very hard to dissolve. Leave overnight and check for undissolved powder before continuing. Filter if necessary. C = n/V = m/Mr/V

Standardizing the DCPIP 1. Pipette a 10 mL aliquot of the ascorbic acid solution into a flask, and titrate against the DCPIP solution (in the burette) to a persistent pink end point (that lasts for 30 seconds). 2. Calculate the concentration of the DCPIP solution:

Titration of Vitamin C in solution with DCPIP 1. Pipette 10.00 mL fruit juice into a conical flask and add about 10 mL distilled water. 2. Titrate the juice against the DCPIP in the burette to a pink end point that lasts for 30 seconds. 3. Calculate the mass of ascorbic acid in 100 mL juice. Reaction is 1:1 n (ascorbic acid) = CV (DCPIP)

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Objective
To employ titration technique to determine the content of vitaminC in commercial tablets using volumetric analysis and compare it with the manufacturers' specifications.
Introduction
Deficiency of essential antioxidant VitaminC in human will lead to scurvy. In this experiment, the vitaminC content of commercial tablets is determined and then compared with the manufacturers' specifications. VitaminC, ascorbic acid C6H8O6, reacts with iodine and is oxidised to dehydroascorbic acid rapidly in acidic medium.
first
Considering iodine is only slightly soluble in water, the above titration cannot be performed directly by a standard iodine solution because of the insignificant end point. Thus, alternative method, back titration, will be employed. Two equations are involved.
First, standard potassium iodate(V) (KIO3), potassium iodate(KI) and dilute sulphuric acis(H2SO4) react to find out the excess quantity of iodine. Below shows the equation.
second
Second, the iodine generated reacts with ascorbic acid immediately. While the excess iodine is the titrated by standardized sodium thisulphate(Na2S2O3) as shown the equation below. Then, the iodine reacted with ascorbic acid can be determined followed by the content of ascorbic acid.
third...

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...CHEMISTRY 221 LABORATORY�QUANTITATIVE ANALYSIS
EXPERIMENT: DETERMINATION OF ASCORBIC ACID IN VITAMINC TABLETS
THEORY:
Ascorbic acid, C6H8O6, MM = 176.13, can be oxidized to form dehydroascorbic acid by bromine via the following reaction:
The bromine or iodine used in the titration is generated by adding an excess amount of KBr or KI to an acidified solution of the sample according to the following reaction:
BrO3- + 5 Br- + 6 H+ 3 Br2 + 3 H2O
IO3- + 5 I- + 6 H+ 3 I2 + 3 H2O
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In the determination of ascorbic acid, both the KBrO3 and KIO3 methods employ a back titration with a standard thiosulfate solution of the excess Br2 or I2 generated by adding a precisely known amount of a primary standard KBrO3 or KIO3 solution to an ascorbic acid solution. In the case of the KBrO3 procedure, potassium iodide is added to react with Br2 to form I2.
Br2 + 2 I- 2 Br- + I2
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I_(2(aq))+〖I^-〗_((aq))↔〖I^-〗_(3(aq))
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...Investigating the vitaminC content of fruits and fruit juice
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Analysis of VitaminC I2 + starch
- 1 -
VitaminC (ascorbic acid) was one of the first vitamins which established a relationship between a disease and its prevention by proper diet. Scurvy has been known for ages. Prevention of scurvy was prescribed by eating fresh vegetables and fruits. The active ingredient in fruits and vegetables that helps to prevent scurvy is ascorbic acid which primates, including humans, cannot synthesize. Ascorbic acid is an important biological antioxidant (reducing agent). It helps to keep the iron in the enzyme prolyl hydroxylase in the reduced form and thereby it helps to maintain the activity of the enzyme. Prolyl oxidase, on the other hand, is essential for the synthesis of normal collagen. In scurvy, abnormal collagen is synthesized that causes skin lesions and broken blood vessels. The minimum daily requirement of vitaminC to prevent scurvy is 30 mg. Some people, including Linus Pauling, advocate mega doses of vitaminC (250-10,000 mg/day) to prevent cancer, the common cold, etc. In this experiment we will determine the vitaminC content of certain foods by titrating the solution with a water soluble form of iodine (I2). VitaminC is oxidized by I2 (as I3– ) according to the following chemical reaction:
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...Investigating VitaminC
Background
VitaminC is found in green vegetables, fruits, and potatoes. It is essential for a
healthy diet. The chemical name for vitaminC is ascorbic acid. Ascorbic acid is a
good reducing agent and therefore it is easily oxidised. Methods for the detection
of vitaminC involve titrating it against a solution of an oxidising agent.
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There are several oxidising agents that can be used and a commonly used one is
2,6-dichlorophenol-indophenol or DCPIP. You need to standardise this against a
known concentration of vitaminC. This means finding out how much DCPIP
reacts with a known amount of vitaminC. You can check the end point colour by
testing a small amount of vitaminC with the DCPIP and observe the
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You will need to find out about the technique of titration and how to make up
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· Investigate the reliability of this method at different concentrations and
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